A conventional viscous fan clutch system consists of a clutch acting as an input member and a fan acting as an output member. Both clutch and fan are on a shaft assembly which drives the input member, in turn powering the output member. As the driving member, the clutch transfers torque to the fan through shearing of a viscous fluid, thus driving the fan. A pumping mechanism and temperature sensor regulate the amount of fluid in the cavity between clutch and fan, thus setting the amount of torque transmitted to the fan through shearing.
Clutches can have different design parameters based on the application. The fan can provide cooling when the engine temperature rises about a threshold temperature. In this case, the clutch and fan are fully engaged to transfer more torque and drive more air in order to cool the engine to the desired temperature. When the engine temperature is below a threshold temperature, the fan clutch can partially disengage, avoiding unnecessary power expenditures from the engine. Instead of a threshold temperature, factors such as delayed or advanced engagement time, valve size or rpm may be used to set clutch and fan engagement.
When a viscous clutch fan assembly fails, parts may be replaced with a compatible repair part. Given the wide range of applications for viscous fan clutches, there are numerous models and makes, each with their own integral mounting systems. In the heavy duty viscous clutch market, manufacturers and dealers may have to build and stock several thousands of different parts to provide replacements for each model of viscous fan clutches, as each model of viscous fan clutch requires model-specific replacement parts.